There are three primary groups of binding systems used in modern cross-country skiing:

* NNN (New Nordic Norm) – including the new R4 NIS variant * SNS (Salomon Nordic System) Profil * SNS PilotFurther variants to NNN and SNS are "BC" (back-country) standards, where the toe hold in the binding is wider and the bar in the boot's toe is longer and thicker in order to give further lateral rigidity. This added strength and rigidity is especially important with the stiffer boots and heavier skis used in backcountry skiing.The existing variety of binding systems, none of which are compatible with the other

The easiest way to tell if they are NNN1 vs. NNN2 is whether they have the dual ridges that extend to the heel. If they do, they are NNN2. If they only have the ridges under the foot and not the heel and have a separate heel plate they are NNN1 (or NNN BC, which is a completely other animal) and won't work with modern boots.